1. Field of the Invention
This invention relates to filtering devices and more particularly to that class utilizing springs as the filter medium.
2. Description of the Prior Art
The prior art abounds with filter devices utilizing tubular screens or springs as a dirt trapping element.
Typical of a tubular screen filter is U.S. Pat. No. 3,584,685 issued on June 15, 1971 to D. M. Boyd, which teaches a tubular screen formed by the helical winding and attachment of a continuous rod member around a plurality of spaced longitudinal bar members in a manner sufficient to provide a continuous helical slot opening of continuously increasing slot width. Thus, the Boyd patent teaches an apparatus suitable for filtering particles of maximum width narrower than the widest slot width.
U.S. Pat. No. 2,342,669 issued on Feb. 29, 1944 to A. C. Hoffman discloses a helically wound spring which is adjustably compressible utilizing an exterior adjustment screw therefor. Openings, of controlled size, are disposed around the periphery of the turns of the spring element by the processes of either etching away portions of the diameter of the spring wire comprising the spring or by building up the thickness of portions of the diameter of the spring wire comprising the spring utilizing the process of plating therefor.